• From: Dallas suburbs. Help me.
  • Registered: 2010-04-21
  • Posts: 145

Topic: Tire tradeoffs - Size versus Treadwear

Can anybody point to comparisons of tire sizes/different treadwear versus lap times on the same car?

Everyobdy goes through this decision I am sure, but I am wondering if it is better to run Star Specs in a tiny 195/60/14 size (pro: low unsprung weight, relatively short wheel tire height, arguably best compound for 190+ treadwear, assume easier on brakes as less rotational inertia and lower diameter than below... con: tiny footprint, easier to heat up.overheat (by how much)? limited traction for acceleration)

Or just buy some ridiculous 17x10 inch wheels and run 300 treadwear tires in a 285/40 (because star specs aren't available in that size). Unsprung weight would really go up, but I assume absolute grip would too (though might be tricky getting higher treadwear tire that wouldn't get greasy as it got hot - if I could even get the thing hot with a 2000 lb car). I think wear would be slower with the big tire too. I imagine this setup would be much much harder on brakes and lose steering feel compared to above.

Questions are vague, but if you have experience on these tradeoffs, I'd love to hear about it. Though the choice is not theoretically binary like I have presented it, these are actually the wheels I have easy access to and if I wasnt really going to go bigger on the footprint, I probably would just run the tiny tires.

  • From: Gilbertsville, PA
  • Registered: 2009-12-22
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Re: Tire tradeoffs - Size versus Treadwear

If you've got power, go big, if not, stay small.

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  • Registered: 2009-09-22
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Re: Tire tradeoffs - Size versus Treadwear

The difference in lap times is statistically insignificant compared to the time you'll spend fixing the car.

But - unless you need to put down a bunch of torque - I'd stay small.

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Re: Tire tradeoffs - Size versus Treadwear

The wider you go the longer they will last and the more traction they will have (well unless you are racing in the rain or snow then you will have less traction)  Of course the bigger an wider the tire the heavier they are and the more rolling resistance which will make you go slower, so you have to find the right balance.

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5 Reply by YesIFit (edited by YesIFit 2010-09-17 06:57 AM)

  • From: DF-Dubya
  • Registered: 2009-08-19
  • Posts: 820

Re: Tire tradeoffs - Size versus Treadwear

If you're looking @ 17" rims, there is a 265/40 Star Spec. Or, why not split the difference and run a 16" rim with a 225/50?

We run a 225/45/17 on our almost 3000lb car and it is plenty of tire. (Would love to get lighter wheels though ... we're running what came with the car and they're ridiculously heavy, but they are 17X8.)

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  • JBgotM
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  • From: Cedar Falls, IA
  • Registered: 2010-07-26
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Re: Tire tradeoffs - Size versus Treadwear

We looked at the same tradeoff for our car. It was either skinny 205 star specs which we felt wouldn't be enough for a 3000# car with good torque. Intead, we chose to go with 255 BFG G-sport. We wish we had the star spec compound, but we accept the trade-offs and get the extra life and less cost.

As Zach said, its fairly insignificant unless you ahave a well sorted car going for an overall win.

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Re: Tire tradeoffs - Size versus Treadwear

As long as the weight of the car isn't overwhelming the tire, always go for the compound first.  In terms of ultimate grip, the smaller Star Spec will have more grip than the big fat 300 treadwear tire, unless your car is so heavy it overheats the smaller tire.

Also, you shouldn't be too worried about overwhelming the tire in straight-line traction with a Lemons car, unless you are making serious power.  A big V8 may have trouble putting the power down, but aside from that, you're probably not spinning tires too much on a road course.  Even the Craptation, which had a pretty torquey 3400 V6 running the front wheels, at around 2500lbs didn't have wheelspin problems.

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  • Troy
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Re: Tire tradeoffs - Size versus Treadwear

We have raced on 225/40r14 Toyo T1Rs (280) and 205/50r15 Star Specs (200).

The Star Specs clocked a slighted faster lap time on an open track.

Racing we were about the same.

Guys on my team felt like the Star Specs had more oversteer.  While a stickier compound, the Toyo had more rubber on the road.

The Toyos are about 21" tall and the Star Specs are about 23."

I'd like to have a 225/50r15 Star Spec but they don't make them.  The 225/50r16 would probably be okay but we would have to buy rims.

While less rotational mass is good, the small 14" tire makes it harder to modulate the brakes.

I considered going crazy with some fat 17s but the tires get pretty pricey too.

Troy

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9 Reply by ifb_mole (edited by ifb_mole 2010-09-18 01:10 PM)

  • Registered: 2009-09-01
  • Posts: 405

Re: Tire tradeoffs - Size versus Treadwear

you can "reverse engineer" into the right tire /  rim.  For example start with the biggest  Star Spec you can get at 17" - 265/40/17 on a 9" - 10" rim or look at the Nitto NT05 tire that has also recieved rave reviews by people (racers, auto X, track days, etc)  In fact the Nitto NT05's are cheaper and people that have run the Star Spec's and the Nitto's give the nod to the NItto's for outright track speed.  Take a look at the Nitto's and they have bigger sizes too like a 275/40/17 or a monster wide 315/35/17

  • From: Dallas suburbs. Help me.
  • Registered: 2010-04-21
  • Posts: 145

Re: Tire tradeoffs - Size versus Treadwear

Great feedback all - thanks for weighing in.

I hadn't thought about the larger diameter tire helping with modulation - foo for thought.

Also, hadn't heard of the Nitto's - I'll look at the straight away.

Torque will be in abundace, and the LSD is only a 25% new, so on my worn out unit, will be close to open diff... so wheelspin is assumed to be an issue (though the car isn't running, so there is no way to know how much of a problem yet) even on the 'well broken in' (over 100,000 mile) motor, torque will be 250 lb/ft or so. Don't know how severe the inside tire lifting will be yet either... so basically I am making decisions on a bunch of assumptions.

Really appreciate the input though... keep it coming if you have more.

Thanks,
Charles

  • JBgotM
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  • From: Cedar Falls, IA
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Re: Tire tradeoffs - Size versus Treadwear

We were spinning the inside wheel when pushing the car. Its a stock 305 with a 255 tire. It doesn't take alot to spin the inside tire on an open diff with torque and lots of body roll.

12 Reply by sergio (edited by sergio 2010-09-18 08:18 PM)

  • sergio
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Re: Tire tradeoffs - Size versus Treadwear

JBgotM wrote:

We were spinning the inside wheel when pushing the car. Its a stock 305 with a 255 tire. It doesn't take alot to spin the inside tire on an open diff with torque and lots of body roll.

If you haven't done it already. Get a bigger front bar and disconnect the rear one. Stiffer front springs & softer rear. See if that helps. Used to have an F-body.

13 Reply by JBgotM (edited by JBgotM 2010-09-19 08:30 AM)

  • JBgotM
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Re: Tire tradeoffs - Size versus Treadwear

sergio wrote:
JBgotM wrote:

We were spinning the inside wheel when pushing the car. Its a stock 305 with a 255 tire. It doesn't take alot to spin the inside tire on an open diff with torque and lots of body roll.

If you haven't done it already. Get a bigger front bar and disconnect the rear one. Stiffer front springs & softer rear. See if that helps. Used to have an F-body.

Yeah we had blown struts end everything. Jay gave us some budget to fix the front suspension so we are getting the bigger bar and stiffer springs from a TRans Am GTA, as well as basic replacement shocks.

Hopefully, the less roll will help keep us from shredding the outside shoulder of the tire. We are currently runnung a little over -2 degrees of camber.

  • From: San Diego, CA
  • Registered: 2010-02-11
  • Posts: 156

Re: Tire tradeoffs - Size versus Treadwear

Wider tires != more traction, just a different contact patch shape (wider instead of longer). 

Tires are round, the weight of the car, combined with the pressure in the tire, will squish the bottom of the tire into a flat spot that touches the road.  Wider tire just means your contact patch shortens, since it wants to squish the tire to make approximately the same contact area.

Now, wider tires generally mean more cornering grip (to a point) given the same compound.  If you've got a lighter car, I'd go with the smaller meats, since the time possibly saved by going to a wider tire is likely exponentially proportional to time lost by nuking the wheel bearings that come with a $500 car, not to mention the rest of the suspension, brakes, etc.

What car and how heavy?

  • From: Dallas suburbs. Help me.
  • Registered: 2010-04-21
  • Posts: 145

Re: Tire tradeoffs - Size versus Treadwear

Car is a 1972 Opel GT with extra motivation.   My example was not only wider, but also significantly taller, and taller tires have longer contact patches (or so I hear).  Also, with the wider tires I assume I could run lower pressures to get maximum contact - this may or may not translate to cars, but when I was young and fit I used to race mountain bikes, and the lowest pressures you could run with good traction were higher with relatively thinner tires, and lower with relatively fat ones. Another MTB analogy would be the taller tire has more contact patch on a 29" MTB wheel than a 26" wheel.  I think that the overall deflection is what you are getting at, and that is a variable but lowering pressure could offset some of that.

Anyway... as of today I am leaning towards smaller tires. The big stuff would certainly eat wheel bearings and brakes as you say.  The rest of the suspension I am less worried about, as I am spending lots of quality time with the lathe and Delrin bar stock making all the squishy bits in the suspension more or less solid. But the overriding thing that has me leaning towards the small tires is unsprung weight - all the big wheels I have access to for cheap are heavy (like 60% heavier , and the tires would be ~ 50% heavier too, which I just haven't been comfortable with). Also, I want the CG to be as low as possible, and putting extra height under the axles seems like a bad idea.

If I had access to cheap ginormous wheels that were not a weight penalty, I would probably go with them. Especially now that ifb_mole made me aware of the Nitto's - I would run them.

I will keep this in the back of my mind and if I ever get the chance to do testing on this theory I certainly will.  Or maybe somebody will come along to this thread who has done it and enlighten us.

Troy, your data is interesting, but not as dramatic a change as what I am thinking of. Your yellow car is very fast I might add.

  • From: Dallas suburbs. Help me.
  • Registered: 2010-04-21
  • Posts: 145

Re: Tire tradeoffs - Size versus Treadwear

Zachreligious wrote:

The difference in lap times is statistically insignificant compared to the time you'll spend fixing the car....

Undoubtedly true... but half the enjoyment is out of benchracing so some (most?) of the decisions are not really to optimize lap times, but to do things because it sounds like the thing to do. With a motor swap in a 40 year old car, I don't think we'll be battling for a win. We are more likely might be begging for a cherry picker and a used main bearing or two in the middle of the night. But I don't want to sit around and think about doing that, I would rather sit around and think about tires and other irrelevant crap.

Now I am off to go get some 40 year old soundproofing tar off the floor...